This invention relates to an electrostatographic printing machine, and more particularly concerns an apparatus for separating a sheet of support material from a heated fuser member employed in the printing machine.
In a typical electrostatographic printing machine, a latent image is recorded on a surface and developed with charged particles. After the latent image is developed, a sheet of support material is positioned closely adjacent thereto so as to receive the particles therefrom. The particles are then permanently affixed to the sheet of support material forming a copy of the original document thereon. Electrographic and electrophotographic printing are differing versions of electrostatographic printing. The process of electrophotographic printing employs a photoconductive member arranged to be charged to a substantially uniform level. The charged photoconductive member is exposed to a light image of an original document. The light image irradiates the charged photoconductive member dissipating the charge in accordance with the intensity of the light transmitted thereto. This records an electrostatic latent image on the photoconductive surface. Electrographic printing differs from electrophotographic printing in that neither a photoconductive member nor a light image of the original document are required to create a latent image on the surface. Both of the foregoing processes generally employ heat settable particles to develop the latent image. The particles are permanently fused to the sheet of support material by the application of heat thereto.
Various techniques have been developed for applying heat to the particles on the sheet of support material. One technique is to pass the sheet of support material with the powder image thereon through a pair of opposed rollers. In one such system, a heated fuser roll and a non-heated back up roll are employed. Preferably, the heated fuser roll has the outer surface thereof covered with a polytetrofluoroethylene commonly known as Teflon to which a release agent such as a silicone oil is applied. The Teflon layer, preferably, has a thickness of about several mils. An alternate approach has been to employ a bare metal heated roll which has a low molecular weight polyethylene applied thereto as a release agent. When heated rolls of this type are employed, the sheet of support material with the toner powder image thereon frequently tends to adhere thereto.
Hereinbefore, various techniques have been devised to strip or separate the sheet of support material from the heated fuser member. One such technique is the utilization of stripper fingers. However, stripper fingers frequently mar the fused toner image adhering to the sheet of support material. Other approaches frequently result in the sheet of support material tending to curl or roll up rather than remaining flat.
Accordingly, it is the primary object of the present invention to improve the apparatus employed to separate the sheet of support material from the fuser member.